Method for producing a peripherally closed hollow profield element

ABSTRACT

The invention relates to a method for producing a peripherally closed hollow profiled element by means of internal high-pressure forming, a hollow elongated blank ( 5 ) being inserted into an internal high-pressure forming tool ( 1 ), and the blank ( 5 ) located completely inside the forming tool ( 1 ) after the insertion being compressed in a region lying between its ends ( 9, 10 ) during the closing operation of the forming tool ( 1 ), after which the compressed blank ( 5 ) is expanded into the final shape of the hollow profiled element by means of fluidic internal high pressure. In order to permit reliable production of the hollow profiled element even during pronounced compression deformations of the blank ( 5 ) of the hollow profiled element, which are produced during the closing of the forming tool ( 1 ), it is proposed that the ends ( 9, 10 ) of the blank ( 5 ) be trimmed before the compression operation, with a respective beveled front face ( 12, 13 ) being formed, and that the trimming contour of the ends ( 9, 10 ) and the beveling angle (α) be selected in such a way that the ends ( 9, 10 ) are deformed by means of the compression operation in such a way that their front faces ( 12, 13 ) have an essentially plane form and assume a position which is as perpendicular as possible to the longitudinal extent of the blank ( 5 ).

CROSS REFERENCE TO RELATED APPLICATION

This application is a national stage of PCT/EP2004/004301 filed Apr. 23, 2004 and based upon DE 103 23 738.0 filed May 24, 2003 under the International Convention.

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to a method for producing a peripherally closed hollow profiled element.

2. Related Art of the invention

A method of the generic type has been disclosed by WO 98/43758 A1. In this case, a blank of a hollow profiled element of uniform cross section is inserted into an internal high-pressure forming tool, the die cavity of which has a reduced cross section relative to the blank in the region between its ends. As a result, the inserted blank of the hollow profiled element is compressed in this region during the closing operation of the forming tool. However, the drawing-in, resulting from this, of the blank of the hollow profiled element manifests itself in inclination or deformation of the end of the blank, this end running rectilinearly at the start of the production process and being disposed with the front face perpendicularly to the longitudinal extent of the blank. On account of the end contour changed by the compression and on account of the tilting of the front face, the axial plungers provided with a conical sealing region and subsequently docking with the ends of the blank can only seal off the blank inadequately relative to the internal high pressure subsequently to be produced. The result of this is that the operation subsequently taking place for expanding the blank by means of the fluidic internal high pressure is not completely reliable and thus the hollow profiled element cannot be produced as desired.

SUMMARY OF THE INVENTION

The object of the invention is to develop a method of the generic type to the effect that reliable production of the hollow profiled element is made possible even during pronounced compression deformations of the blank of the hollow profiled element, which result during the closing of the forming tool.

The invention is based on the knowledge that the deformations occurring during the compressing of the blank can be compensated for by the blank ends being cut to size in a specific manner. The trimming according to the invention of the blank ends achieves the effect that, after the compression and when the forming tool is completely closed, the front faces of the ends are flat and are as far as possible oriented perpendicularly to the longitudinal extent of the blank. As a result of the position of the blank ends which is achieved, the axial plungers can dock with these ends as if the blank had not been trimmed and had not been subjected to compression beforehand. The axial plungers can therefore sufficiently seal off the blank at both ends relative to the internal high pressure still to be produced, as a result of which reliable production of the hollow profiled element is made possible. In addition, a chip-removing collision between the axial plungers and the blank otherwise provided with tilted front faces is avoided by the invention, the chips and slivers which are produced in the process having to be removed in a complicated manner during a rework operation after removal of the finish-formed hollow profiled element. This removal usually involves severing of the sealing sections of the blank ends, so that such a trimming operation can be dispensed with on account of the invention, it being possible, in addition to saving labor, to save material scrap difficult to dispose of. It is also no longer necessary to plan in advance for a lost additional length of the blank, as a result of which the friction between blank and forming tool to be overcome during the subsequent expansion of the blank by means of internal high pressure is considerably reduced on account of the shorter length of the blank.

In a preferred embodiment of the invention, the ends of the blank are trimmed in such a way that the front faces of the ends are beveled relative to the center axis lying in the compression direction and running transversely to the longitudinal axis of the blank. This trimmed form results from the additional knowledge that the deformations of the blank which are produced by the compression as a function of the compression direction lead to inclination of the tube end cross section and thus of the front face relative to said axis, so that the tube ends are beveled in the opposite direction within the scope of the invention. During the aforesaid inclination of the cross section, a top peripheral region of the tube end projects beyond its bottom peripheral region in the axial direction.

In a further preferred development of the invention, the blank ends are trimmed in such a way that their front faces remain arranged parallel to one another. In the event of the end regions of the blank of the hollow profiled element coming to lie vertically offset relative to one another after compression has been effected, the front face of the one untrimmed end is tilted upward, so that the bottom peripheral region projects axially beyond the top peripheral region of the end, and the front face of the other untrimmed end is tilted downward, the top peripheral region of the end projecting beyond the bottom peripheral region in the axial direction. The blank can therefore be trimmed at both ends at the same angle in the opposite direction of the tilting before the compression operation. The resulting homogeneity of the trimming at the same time makes the work during the cutting process easier. In addition, the same applies to a lateral offset of the ends after compression has been effected.

An especially preferred embodiment of the invention, constitutes the specific determination of the beveling angle of the trimming, which lies within a range of between 6° and 10°, preferably 8°. In this respect, practical and theoretical investigations have shown that the tilting of the front faces which is caused by the compressing deformation virtually always lies within this angular range, so that an equally large beveling angle of the front face of the end has to be provided in the opposite direction during the trimming.

According to a further preferred embodiment of the invention, the end deformation actually occurring due to the subsequent compression operation is determined by a computer simulation, in particular a finite-element simulation, before the trimming of the ends and then an optimum trimming contour and an optimum beveling angle of the trimming to be effected is precisely calculated therefrom for compensating for the deformation. In this way, the beveling angle and trimming contour suitable for each component and for every type of compression can be determined individually relatively easily without resorting to numerous, laborious, empirical investigations.

According to a further preferred embodiment of the invention, the trimming of the ends is effected two-dimensionally. In this case, although the exact spatial contour of the blank end is not covered, such trimming can be carried out in an especially economical manner with respect to the method and quickly.

In an especially preferred embodiment of the invention, the trimming of the ends is effected by a three-dimensional contour cut. This may be effected, for example, by means of a cutting laser and offers the best connecting area imaginable to the axially docking plungers, so that optimum sealing is achieved by means of the plungers.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail with reference to an exemplary embodiment shown in the drawings, in which:

FIG. 1 shows a lateral half section of a blank of a hollow profiled element trimmed on both sides according to the invention, in an opened forming tool,

FIG. 2 shows a lateral half section of the blank of the hollow profiled element from FIG. 1 after the compression operation has been effected, in a closed internal high-pressure forming tool.

DETAILED DESCRIPTION OF THE INVENTION

Shown in FIG. 1 is an internal high-pressure forming tool 1 which consists of a top part 2 and a bottom part 3. The tool die cavity 4, which is formed by both tool parts 2 and 3 and defines a forming space for a blank 5 of a hollow profiled element to be formed which is inserted into the tool 1, is designed in such a way that one end 6 of the die cavity 4 is arranged vertically offset relative to the other end 7. In the closed forming tool 1 according to FIG. 2, these two ends 6 and 7 of the die cavity have approximately the same diameter as the inserted blank 5 of the hollow profiled element. The die cavity 4 is considerably constricted in cross section in a center region 8, which connects the two ends 6 and 7 to one another.

The blank 5 of the hollow profiled element has in turn, at its two ends 9 and 10, a respective front face 12 or 13 inclined in the direction of the longitudinal axis 11 of the blank 5 of the hollow profiled element. Whereas a top peripheral region of the front face 12 projects beyond its bottom peripheral region 15 in the axial direction, a bottom peripheral region of the front face 13 projects beyond its top peripheral region 17 in the axial direction. The blank 5 of the hollow profiled element, in which the front faces 12 and 13 of its ends 9 and 10 are arranged parallel to one another, is located completely inside the die cavity 4 of the forming tool 1. The beveling angle a of the front face 12 or 13, respectively, relative to the center vertical axis 18 is 80.

To produce the hollow profiled element, first the ends 9 and 10 of the blank 5 are trimmed in such a way that beveled front faces 12 and 13 are obtained, in which case the latter are where possible to be beveled relative to the axis lying in the compression direction in order to obtain an optimum deformation result from the compression operation, and thus in order to ensure sound sealing of the axial plungers docking subsequently for the internal high-pressure forming. In this exemplary embodiment, the blank ends 9 and 10 are trimmed in such a way that their front faces 12 and 13 remain parallel to one another. In order to permit the desired trimming, the deformation of the ends 9 and 10 which is caused by the subsequent compression operation is determined before the trimming operation in a finite-element computer simulation and then the suitable trimming contour and the suitable beveling angle α is calculated therefrom. The blank 5 of the hollow profiled element trimmed in this way is now inserted into the die cavity 4 of the forming tool 1, after which the latter is closed. On account of the center region 8 which constricts the die cavity 4, the blank 5 of the hollow profiled element is compressed during the closing operation of the forming tool 1 by the top part 2 and the bottom part 3 moving toward one another. The center compression 19, which can be seen from FIG. 2, which shows the forming tool 1 in its closed state, acts on the ends 9 and 10 of the blank 5 of the hollow profiled element in such a way that the front faces 12 and 13 of the blank 5 are disposed perpendicularly to its longitudinal extent. The axial plungers are then moved up to the ends 9 and 10 of the blank 5 of the hollow profiled element and seal the latter with a conical sealing region. Via the axial plungers, a pressure fluid is now directed into the blank 5 of the hollow profiled element and put under high pressure. On account of the internal high pressure present, the blank 5 of the hollow profiled element is expanded, in the course of which it abuts fully against the die cavity 4 of the forming tool 1. The pressure fluid is now relieved and directed out of the now finish-formed hollow profiled element, after which the axial plungers are retracted from the forming tool 1. Finally, the latter is opened and the hollow profiled element is removed from the die cavity 4.

Apart from that, it may be emphasized at this point that blank material can be pushed up axially by means of the axial plungers during the internal high-pressure forming. For this purpose, the invention has the considerable advantage that the straightening of the front faces 12, 13 makes possible a homogeneous introduction of force by the axial plungers into the forming region, to be bulged out, of the internal high-pressure forming process, a factor which, due to the fact that this consequently avoids undesirable fold formations and material thickening, makes an exceptional contribution to the reliability of the process. 

1. A method for producing a peripherally closed hollow profiled element by means of internal high-pressure forming, comprising: inserting a hollow elongated blank into an internal high-pressure forming tool, the blank located completely inside the forming tool after the insertion being compressed in a region lying between its ends during the closing operation of the forming tool, after which the compressed blank is expanded into the final shape of the hollow profiled element by means of fluidic internal high pressure, wherein the ends (9, 10) of the blank (5) are trimmed before the compression operation, with a respective beveled front face (12, 13) being formed, and wherein the trimming contour of the ends (9, 10) and the beveling angle (a) are selected in such a way that the ends (9, 10) are deformed by means of the compression operation in such a way that their front faces (12, 13) have an essentially plane form and assume a position which is as perpendicular as possible to the longitudinal extent of the blank (5).
 2. The method as claimed in claim 1, wherein the trimming is effected in such a way that the front faces (12, 13) of the ends (9, 10) are beveled relative to the center axis (18) lying in the compression direction and running transversely to the longitudinal axis (11) of the blank (5).
 3. The method as claimed in claim 1, wherein the blank ends (9, 10) are trimmed in such a way that their front faces (12, 13) remain arranged parallel to one another.
 4. The method as claimed in claim 1, wherein the beveling angle (α) lies within a range of from 6° to 10°.
 5. The method as claimed in claim 1, wherein the end deformation occurring due to the subsequent compression operation is determined by a computer simulation before the trimming of the ends (9, 10) and then a trimming contour and a beveling angle (α) of the trimming to be effected is calculated therefrom for compensating for the deformation.
 6. The method as claimed in claim 1, wherein the trimming of the ends (9, 10) is effected two-dimensionally.
 7. The method as claimed in claim 1, wherein the trimming of the ends (9, 10) is effected by a three-dimensional contour cut.
 8. The method as claimed in claim 1, wherein the beveling angle (α) is 8°. 